I have received my H4EAD card yesterday. I am not sure what is my next step.. How do I apply for my SSN & what has to be done with my old ITIN. Also is there anything else that has to be done before I start looking for a job.

You will have to submit an AR-11 form. The first question on it is "Is this change of address for an application or petition currently in progress?" select "Yes" & submit your request. It can be done online too